The present invention relates generally to rapid prototyping systems, specifically, 3D printing systems for making multiple layered dental devices such as, for example, artificial teeth, dentures, splints, veneers, inlays, onlays, orthodontics, aligners, retainers, copings, frame patterns, crowns and bridges, models, appliances and the like. More particularly, it is related to the use of ink-jet, fused deposition modeling (FDM), selective laser sintering (SLS), stereolithography (SLA), digital light processing (DLP) or their combinations to build-up the dental devices as three-dimensional objects from many material systems and novel resin systems of this invention. Ink-jet printing system dispenses materials through ink-jet printing head to form 3D object, which harden by cooling, polymerization, and light irradiation. FDM extrudes thermoplastic materials throughout nozzle to build 3D object. SLS uses laser as power source to sinter powdered materials to form solid objects. SLA using laser beam traces out the shape of each layer and hardens the photosensitive resin in a vat (reservoir or bath). DLP system builds three-dimensional objects by using the Digital Light Processor (DLP) projector to project sequential voxel planes into liquid resin, which then caused the liquid resin to cure.
In general, rapid prototyping refers to a conventional manufacturing process used to make parts, wherein the part is built on a layer-by-layer basis using layers of hardening material. Per this technology, the part to be manufactured is considered a series of discrete cross-sectional regions which, when combined together, make-up a three-dimensional structure. The building-up of a part layer-by-layer is very different than conventional machining technologies, where metal or plastic pieces are cut and drilled to a desired shape. In rapid prototyping technology, the parts are produced directly from computer-aided design (CAD) or other digital images. Software is used to slice the digital image into thin cross-sectional layers. Then, the part is constructed by placing layers of plastic or other hardening material on top of each other. There are many different techniques that can be used to combine the layers of structural material. A final curing step may be required to fully cure the layers of material for some of the techniques. The application of sealer may be needed to form a dense 3D objects for some of the techniques, such as inkjet printing of a powder bed or FDM. Additional milling may be added to some of the techniques too.
Ink-jet printing technology is a rapid prototyping method that can be used to fabricate the three-dimensional object. In one well known ink-jet printing method that was developed at Massachusetts Institute of Technology, as described in Sachs et al., U.S. Pat. No. 5,204,055, printer heads are used to discharge a binder material onto a layer of powder particulate in a powder bed. The powdered layer corresponds to a digitally superposed section of the object that will be produced. The binder causes the powder particles to fuse together in selected areas. This results in a fused cross-sectional segment of the object being formed on the platform. The steps are repeated for each new layer until the desired object is achieved. In a final step, a laser beam scans the object causing the powdered layers to sinter and fuse together if needed. In another ink-jet printing process, as described in Sanders, U.S. Pat. Nos. 5,506,607 and 5,740,051, a low-melting thermoplastic material is dispensed through one ink-jet printing head to form a three-dimensional object. A second ink-jet printer head dispenses wax material or other supporting material to form supports for the three-dimensional object. After the object has been produced, the wax supports are removed, and the object is finished as needed. MultiJet printers, such as, the high-quality PolyJet and MultiJet 3D printing processes use a UV light to crosslink a photopolymer. However, rather than scanning a laser to cure layers, a printer jet sprays tiny droplets of the photopolymer (similar to ink in an inkjet printer) in the shape of the first layer. The UV lamp attached to the printer head crosslinks the polymer and locks the shape of the layer in place. The build platform then descends by one layer thickness, and more material is deposited directly onto the previous layer. Triple-jetting technology (PolyJet) used in Stratasys Objet 500 Connex3, is the most advanced method of PolyJet 3D printing. This technology performs precise printing with three materials and thus makes three-color mixing possible.
Fused deposition modeling (FDM) technology was developed and implemented at first time by Scott Crump, Stratasys Ltd. founder, in 1980s. What is good about this technology that all parts printed with FDM can go in high-performance and engineering-grade thermoplastic. FDM is the only 3D printing technology that builds parts with production-grade thermoplastics, so things printed are of excellent mechanical, thermal and chemical qualities. 3D printing machines that use FDM Technology build objects layer by layer from the bottom up by heating and extruding thermoplastic filament. Along to thermoplastic a printer can extrude support materials as well. Then the printer heats thermoplastic till its melting point and extrudes it throughout nozzle to a build platform. To support upper layer the printer may place underneath special material that can be dissolved after printing is completed. When the thin layer of plastic binds to the layer beneath it, it cools down and hardens. Once the layer is finished, the base is lowered to start building of the next layer. This technology is considered to be simple-to-use and environment-friendly. Different kind of thermoplastics can be used to print dental objects.
Selective Laser Sintering (SLS) is a technique that uses laser as power source to form solid 3D objects. This technique was developed by Carl Deckard, a student of Texas University, and his professor Joe Beaman in 1980s. The main difference between SLS and SLA is that it uses powdered material in the vat instead of liquid resin as stereolithography does. Unlike some other additive manufacturing processes, such as stereolithography (SLA) and fused deposition modeling (FDM), SLS doesn't need to use any support structures as the object being printed is constantly surrounded by unsintered powder. Due to wide variety of materials that can be used with this type of 3D printer the technology is very popular for 3D printing customized products. SLS requires the use of high-powered lasers, which makes the printer to be very expensive. Extensive surface finishing is required for dental objects made with this process.
SLA 3D printing method was patented by Charles Hull, co-founder of 3D Systems, Inc. in 1986, which converts liquid plastic into solid 3D objects. SLA 3D printers work with excess of liquid resin that hardens and forms into solid object by irradiation. Parts built usually have smooth surfaces but its quality very depends on the quality of SLA machine used. After plastic hardens a platform of the printer drops down (top down printer) or move up (bottom up printer) in the tank a fraction of a millimeter and laser forms the next layer until printing is completed. Once all layers are printed the object needs to be rinsed with a solvent and then placed in a post-cure oven to finish processing.
Digital Light Processing is another 3D Printing process very similar to stereolithography. The DLP technology was created in 1987 by Larry Hornbeck of Texas Instruments and became very popular in Projectors production. It uses digital micro mirrors laid out on a semiconductor chip. 3D inkjet, DLP and SLA all works with photopolymers. The difference between SLA and DLP processes is a different light source. DLP method projects sequential voxel planes into liquid resin, which then caused the liquid resin to cure. The material to be used for printing is liquid resin that is placed in the transparent resin container. The resin hardens quickly when affected by irradiation of light. The printing speed is pretty impressive, especially with Carbon3D's CLIP (Continuous Liquid Interface Production) technology. The layer of hardened material can be created with such printer in a few seconds. When the layer is finished, it's moved up and the next layer is started to be worked on. CLIP technology balances light and oxygen to eliminate the mechanical steps and layers that are the standard DLP process step and allow the production of commercial quality objects at high speed.
This invention provides digital dental devices using computer-aided 3D printing methods as mentioned above. In particular, it is related to designing and manufacturing two or multiple layered dental devices or dental prostheses, such as partial, full dentures or other prosthetic devices, specifically, printing partial, full dentures, surgical guides, nightguards, flippers, splints, orthodontic devices, aligners, retainers, crowns, bridges, partial or full denture bases using computer aided design and printing methods.
Dental devices, specifically for example, denture base and denture tooth should exhibit certain desirable physical characteristics to be suitable for use and offer desirable benefits to patients. They should be dimensional stable for effective functioning, sufficient strength to withstand masticating stresses and resistant to abrasion and chipping during use. They also should be durable and stable to solvents, foods, water, cold and hot and maintain esthetics without discoloration. In addition, they should be esthetics to mimic natural dentition and gum with esthetically acceptable color, i.e., close to that of natural dentition and gum. The denture base and denture tooth should not wear or deform out of occlusion, and denture base should be capable of being bonded firmly to artificial teeth. They should also be adjustable to ordinary means of physical shaping, grinding, and polishing. Denture base and denture tooth materials should be stable without discoloration and provide consistent handling properties during their shelf life. Denture fabricated from denture base and denture tooth materials should provide function, comfort and fit to the patients. It is desirable that denture base materials are compatible with hard and soft mucosal tissues. So it is desirable that denture base contains at least two different materials with different physical and mechanical properties. It is preferable that denture can be easily adjustable to provide better retention, better occlusal contact and better fit so as to provide better function, comfort and performance for patient. It is also preferable that denture can be locally adjustable while other parts remain unchanged.
Typically, denture bases are methacrylate-based acrylics, thermoplastic based or light curable resin based. Most common denture tooth materials are also methacrylate-based acrylics. In general, methacrylate-based acrylics denture bases and teeth are made out of dough from the blending of PMMA or modified PMMA polymer powders with MMA or modified MMA liquids. Denture teeth are commonly made in a tooth manufacturer. Dental lab typically uses denture teeth and denture base material from manufacturer to make denture for patient. The initial step(s) commonly used in the making a denture by making a final impression of a patient's mouth. A cast (or record base) is made of the final impression of a patient's mouth. Typically the cast is made of plaster. Then wax is shaped into the form of a denture base on the cast of the patient's mouth and artificial teeth are positioned into the denture base shaped wax. The denture base shaped wax with the artificial denture teeth is then positioned in an articulator. The artificial teeth in the denture base shaped wax are then articulated. The articulated denture base shaped wax with the artificial teeth is then positioned in a flask. The volume of the flask is filled with hardenable investment material, such as plaster. After the investment material hardens the wax is eliminated, for example by heating the flask in boiling water, leaving the artificial teeth supported by the investment material and a denture base shaped mold cavity within the investment material. After a thorough cleansing of the mold cavity, a denture base material is introduced into the mold cavity. The denture base material then hardens to form a denture. The process to make a denture is long, time-consuming and labor intensive.
Preparation of full and partial dentures typically requires several dental office visits by each patient. The visits include labor intensive processes such as the construction of the base-plate and occlusion rims, wax try-in, invest the wax-up, wax removal and compression packing or pouring of denture base acrylic as described early. This traditional method typically resulted in a denture base containing homogeneous denture base material, which supported artificial denture teeth. A method of using light polymerizable wax like material (Eclipse system sold by Dentsply International) reduces the dental office and laboratory visits and the labor involved in making the denture, which provides a process for making a denture, comprising: articulating artificial teeth while supported by polymerizable material, whereby a denture comprising said artificial teeth is provided without forming a mold for making tooth setup volume of a denture base. The process is completed without forming wax and without applying inorganic plaster to the artificial teeth. Multiple layers of denture base materials are possible and are included in the denture base by this method.
Most recently, 3D printing systems have been using to make denture base and denture. Various 3D printing materials are used for 3D printing to make denture base and denture. Using acquired digital data, a 3D printer prints materials to form final denture with denture base and denture teeth made from different materials. A 3D printer may also print material to form desired denture base, where commercially available artificial denture teeth are subsequently placed into printed cavities and bonded to this denture base. Separately, some denture teeth are also printed by a 3D printer and used to place into printed cavities and bonding to the printed denture base. Dentca's 3D Denture Base System scans the impression and builds denture base layer by layer using a stereolithographic laser printer and then bonds plastic teeth and final cures in a light chamber. FDM 3D printing method prints a denture using FDM printer with scanned or CAD data, which extrudes and deposits molten thermoplastic in layers to build denture from bottom up. Each layer of molten thermoplastic material is deposited on top of previous one and flattened slightly by the extrusion head. The layers are fused together to form final denture base.
Even though current 3D printing methods are very promising, there are still no consistently reliable 3D printing methods and materials to replace the current proven and established methods and materials for denture fabrications by dental laboratory technicians. Conventional denture fabrication process incorporates several steps to ensure the accuracy and functionality of each denture. Nevertheless, some of 3D printing methods required complicated process to obtain digital data. The fabricated denture may not fit in patient's mouth and teeth may not occlude correctly, additional adjustment or reline is needed that can be labor intensive and painful process. Unstable bites on the denture will result in a poor fit. Denture may need to be remade that cost time, money and delay the patient care. Excessive grinding of teeth and denture base may be needed to achieve desired occlusion, which will result in the loss of esthetics of both fabricated denture base and artificial denture teeth and require additional finishing and polishing. It also faces the potential of grinding away more wear resistant enamel layers which commonly existed in some of artificial denture teeth and exposed the less wear resistant dentin layer. In order to avoid above issues, manufacturers and labs often make a try-in denture for the patient. After tried-in, adjusted and confirmed, and then duplicated the tried-in denture by printing or other fabrication methods, which adds additional steps back and requires additional office visits.
It is desirable the denture fabricated can be adjusted during final denture try-in to obtain desirable occlusion without the need of excessive of remaking, grinding, finishing and polishing. A denture fabricated where artificial denture teeth can be adjusted is highly desirable, which can avoid the need of additional tried-in step. It is also desirable the denture fabricated can be comfortable fit perfectly into oral cavity with rigid area to support artificial denture teeth and soft or relatively flexible contact surface to mucosal area for comfort and fit. Typically, denture bases are PMMA based acrylics. However, PMMA and MMA based denture bases have the disadvantage of being subject to brittle fracture due to the nature of PMMA. Rubber impact modified PMMA acrylics were used to improve their fracture toughness and impact strength. Full denture is typically formed from a rigid material since it is needed to support the artificial teeth chewing function without any movement during action. Flexible partial dentures, typically made of flexible thermoplastics, such as Nylon 12, acetal resin, etc. are being commonly used for patients, which provide comfort due to their compliance and flexibility. The use of clasps enables to stabilize the artificial denture teeth in place. The resilience and flexibility of these denture bases are limited due to the need to support artificial denture teeth. Significantly improved resiliency of tissue contact surface is desirable without compromising the artificial denture teeth stability during mastication. It is desirable to have a denture that provides a rigid ridge to support artificial denture teeth in position and resilient and flexible contact layer/area to patient's soft mucosal area for comfort and fit, which is more compatible to patient's oral cavity containing rigid ridge area and soft mucosal area. It is also desirable to have a partial denture that provides a rigid ridge to support artificial denture teeth in position, toughening clasps to stabilize the partial denture in place, and resilient and flexible contact layer/area to patient's soft mucosal area for comfort and fit, which is more compatible to patient's oral cavity containing remaining teeth, rigid ridge area and soft mucosal area. Common practice to improve the patient's comfort and fit is to reline a denture with a soft reline material, which requires additional labor intensive step. It is desirable to provide an integrated denture incorporating a soft layer onto rigid denture base or having two or more areas that offer different performances including a tooth adjustable area. In addition, it is desirable that the contact surface of denture to mucosal area can be adjusted easily to get better fit. It is also desirable that the contact surface of denture to mucosal area can be adjusted and re-adjusted as needed, such as the need due to the ridge resorption over time. An adjustable polymer layer or a shape memory polymer is especially desirable to be used here. When digital intraoral scan is used for the fabrication of denture or denture base, a digital designed tissue side of denture may not perfectly fit to the oral cavity of the patient due to intraoral scanning involving soft tissues and an adjustable polymer layer or a shape memory polymer layer at tissue side allows the denture to be easily adjusted to fit the oral cavity of the patient to get the best fit and comfort. It is also desirable to have a denture, where limited tooth adjustment can be easily achieved. Denture base material around denture teeth can be easily adjusted at elevated temperature or other conditions is preferred.
Even though this invention referred mainly to denture, denture base and teeth, the printing methods and materials of this invention are not limited to the printing of denture, denture teeth or denture base, they can be used to print various dental devices. Their shades can be formed from clear to highly pigmented shade. For example, a multiple layered nightguard can be printed, where the hard and wear resistant top surface layer can effectively withstand wearing and grinding while flexible or resilient side or not occlusal contact part in nightguard can provide comfort, retention and easy insertion and easy removal for the patient. The denture base or denture tooth materials mentioned in this invention can be easily referred as dental materials, such as restorative materials, night guard materials, retainer materials, or aligner materials, etc.
Leyden et al., U.S. Pat. Nos. 6,660,209 and 6,270,335 disclose an ink-jet printing method using commercial print heads having multiple orifices (jets) to selectively fire droplets of hot melt, radiation-curable material onto a substrate. Each orifice can be equipped with a piezoelectric element that causes a pressure wave to propagate through the material when electric current is applied. The print head moves along a scan path selectively depositing the flowable material onto the substrate. In a subsequent step, light radiation is used to cure the material.
Yamane et al., U.S. Pat. No. 5,059,266 discloses an ink-jetting method, whereby a photosetting or thermosetting resin is jetted along a flight passage of the material to a stage to thereby laminate the material on the stage, changing at least one of a jetting direction of the material along the flight passage and a jetting amount of the material, thereby controlling a jetting operation of the material, and exposing the laminated material to light to cure the material, thereby forming the article.
Bredt et al., U.S. Pat. No. 5,902,441 describes another ink-jet printing method, which involves applying a layer of powder particles containing an activatable adhesive onto a flat surface that can be indexed downward. The ink-jet printer introduces an activating fluid onto to the layer of particles in a predetermined pattern. The fluid activates the adhesive in the mixture, causing the particles to adhere together in an essentially solid layer. After the first cross-sectional portion of the article is formed, the movable surface can be indexed downward. Successive layers of the mixture of particles are applied in the same manner to form the desired article.
Oriakhi et al. discloses in US Patent Application Publication No. US 2005/0082710 an ink-jet printing method, wherein a particulate blend of reactive glass ionomer particulates, cross-linkable polyacid particulates including polyvinyl pyrrolidone-co-polyacrylic acid, and nanocomposites is spread in a fabrication bin. An ink-jet printer applies an aqueous phase binder onto a predetermined area of the particulate blend to form hydrated cement. A glass-ionomer chemical reaction causes the hydrated cement to harden.
Kapserchik et al. discloses in US Patent Application Publication No. US 2004/0094058 an ink-jet printing system using acid-base cements. Layers of powder particulate are deposited on a flat surface. The powders include a base such as a metal oxide or an aluminosilicate glass, a polymeric acid or other acid. The ink-jet printer dispenses an aqueous binder. The basic powder interacts with the acid in the presence of water, causing the formation of an ionically cross-linked hydrogel salt. Formation of the cross-linked hydrogel causes setting of the mixture.
More particularly, ink-jet printing methods for making three-dimensional dental products have been developed and are described in the patent literature. For example, Moszner et al., U.S. Pat. No. 6,939,489 discloses a process for fabricating three-dimensional dental form pieces for dental restoration and replacement parts using three-dimensional plotting technology. The object is produced in a layered manner by the cutting away of micro drops or micro cords discharged from nozzles in the three-dimensional plotter. The discharged material can be hardened by a variety of mechanisms depending upon the type of material used. This includes cooling of melted material, polycondensation, polyaddition, or thermal-curing, and light radiation. In the '489 Patent, the three-dimensional plotting technology is described as being different than conventional rapid prototyping (selective laser sintering, 3D printing, and stereolithography).
Rheinberger et al., U.S. Pat. No. 7,189,344 discloses a process for producing three-dimensional dental restorative parts, such as full or partial dental prosthesis, using ink-jet printers that are used in the ink-jet printing methods developed by MIT as described above. The process involves spraying a polymerizable material onto a base support in a layer-by-layer manner. Each layer of material is polymerized by a light source prior to the application of the next layer. The polymerizable material is described as being wax-like having up to 70% by weight of at least one of a polymerizable monomer and oligomer; from 0.01 to 10% by weight of a polymerization initiator; and at least 20% by weight of a mixture having a selected one of a wax-like and flowable monomer and a color pigment.
Feenstra, U.S. Pat. Nos. 6, 921,500 and 6,955,776 disclose an ink-jet printing process for making dental elements such as crowns using a liquid binder and powder bed. The element is produced by applying successive layers of powder and discharging the liquid binder onto the layers using an ink-jet printer. The binder preferably includes nanomeric, inorganic solid particles having polymerizable and/or polycondensable organic groups at their surface. After the binder has been applied to the last layer of powder, any excess, unbound powder is removed. Then, the powdered layers are sintered by heating to a temperature in the range of about 400 to 800° C. The sintering step is performed so that only necks between the powder particles are formed. The resulting sintered dental element is infiltrated by a second phase material, such as glass-ceramic or polymer, which melts at a lower temperature than the material of the dental element. This reduces the porosity of the dental element.
Bordkin et al., U.S. Pat. No. 6,322,728 discloses an ink-jet printing process for making dental restorations by printing a binder into layers of powder. The process involves depositing a layer of ceramic or composite powder material onto a powder bed. The design of the restoration is based on a CAD representation. A binding material is applied onto the ceramic or composite layer. This application of powder/binder material is repeated several times to produce the desired shape of the restoration. After the layering process is completed, the structure is cured to further promote binding of the particles.
The present invention provides novel high strength/toughness, resilient or high toughness liquid resin/composite systems for fabricating three-dimensional dental devices using the Inkjet, Digital Light Processor (DLP) projectors or stereolithography. This invention can also use many commercially available materials, such as polymerizable resins, thermoplastic materials, shape memory polymers, etc., their combinations and their combinations with liquid resin/composite systems of this invention and several early inventions of present inventor(s) for fabricating three-dimensional dental devices using the Inkjet, FDM, DLP, SLS, SLA or their combinations. Although the Inkjet, DLP or SLA method and high strength/toughness, resilient or high toughness materials are described primarily herein as being used to make a layered dental prosthesis, such as splint, aligner, full and partial denture, denture base and artificial teeth, etc., it should be understood that this is for illustration purposes only. The inkjet, DLP method or SLA method using high strength/toughness, resilient or high toughness materials can be used to make any dental device such as, for example, artificial teeth, dentures, orthodontics, splints, veneers, inlays, onlays, copings, frame patterns, retainers, aligners, flippers, night guards, sport guards, crowns and bridges and the like. We have provided a general description of these methods using high strength/toughness, resilient or high toughness material systems as follows. (A more detailed description of the methods and high strength/toughness, resilient, or high toughness materials used to make the dental devices is set forth below.)
In this method, a polymerizable liquid resin material or heated resin material as a liquid is loaded into a resin bath of a 3D printer based on a DLP method, SLA method or a combination of DLP and SLA. In the case of using DLP method, it builds 3D objects by projecting sequential voxel planes into liquid resin (or heated liquid resin), which then polymerizes it to solid. Successive layers of polymerized material are added in this manner until the device is completely fabricated. Multiple light (or laser) sources may be used with these methods. Once first object was built with successive layers of first polymerized material, subsequent successive layers of second polymerized material may be added to first polymerized object by these methods, which typically require the projecting sequential voxel planes into liquid resin (or heated liquid resin) from top down or tilted angle. Similarly, additional polymerized materials can be built on above objects having two or more polymerized materials to form final two or more layered device. Then the device, for example, a denture, is washed, finished and fully final cured as needed. The fully cured and polished denture is now ready to be used by the patient. In the case of two layered aligner or splint, two clear vats of polymerizable liquid resin materials might be used and built up the devices layer by layer. Moreover, two or more parts may be printed out separately with different materials and then bonded them together to form final objects (or dental devices). Printed out different material layers (parts) may also be finally cured together to form layered objects (or dental devices).